SAN FRANCISCO -- Microsoft ( MSFT) said sales of its Halo 3 video game topped $300 million worldwide in its first week on the market, amid swirling rumors that the software giant's close relationship with the game's maker may be coming to an end.The popular game series, which is exclusively developed for Microsoft's Xbox 360 game player, was developed by Bungie Studios and published by Microsoft. Several game blogs were trying to confirm a rumor this week that Bungie may be breaking from the Redmond, Wash., software company or planning on developing games for competing platforms. Bungie reportedly has declined to comment, while Microsoft denies the rumor. Sales of the Xbox device have now doubled above their weekly average from before the launch of Halo 3, according to Microsoft. Microsoft was up 15 cents to $29.60.